Museum vice-president Janette Buckingham said the discovery had come as a shock.
“It is quite surreal because none of us had any idea.
“Even looking up our records would not have told us.”
She had been told the acid was a potential hazard “but there is nothing to say it was going to blow up in our faces’’.
June Leith, a volunteer at the museum for eight years, said she would have dusted the acid container during the years.
“It is a bit scary after hearing what it was.”
Southland District Council publications specialist Chris Chilton said that for the past several years staff had been checking inventory at museums to look for items that could potentially become unstable overtime.